A major difficulty for handling call routing in a mobile communication network is due to subscriber mobility. A mobile subscriber can roam freely from the service area of one switch to that of another. Hence, the switch which serves the mobile subscriber—providing switching functions including call routing—may change from time to time. However, from the perspective of the calling subscriber, the change in the serving switch of the recipient subscriber is invisible. Whether the recipient subscriber is located within the service area of his “home” switch, i.e., the switch at which the recipient subscriber registers with the mobile communication network, or is under the service of a different switch, the calling subscriber always dials one and the same telephone number, or directory number, of the recipient subscriber. This number is usually called the Mobile Subscriber ISDN (MSISDN).
In order to route the call to the recipient subscriber, the switching system of the mobile communication network internally assigns a temporary number to the call and uses this number to route the call to the terminating switch of the call, that is, to the particular switch which serves the recipient subscriber at the time of the call. The temporary number, which is different from the MSISDN, is often called the Mobile Station Roaming Number (MSRN). MSRNs are usually related to the geographical numbering plan and are neither assigned to nor visible to any subscriber. An assigned MSRN remains temporarily associated with the call until the call is properly routed to the terminating switch. In short, by means of the MSRN (temporarily) associated with a mobile terminating call, the switching system of the mobile communication network can route the call to the terminating switch serving the recipient subscriber.
A similar mechanism is used for handovers, in which case the temporary number is termed as a Handover Number (HON). For a handover from an anchor switch to a non-anchor switch, HONs fulfill the similar purpose and use the similar mechanism as MSRNs described above.
In the context of the present disclosure, both MSRNs and HONs are examples of call-routing numbers as they both serve to route, or direct, a call to its destination. Call-routing numbers are usually administered in series. Each call-routing number series comprises a certain amount of call-routing numbers. Conventionally, this certain amount may be fixed, e.g., 100.
With the development of distributed computing, more and more switches in mobile networks are being implemented as distributed systems, also called switch clusters. In the language of distributed computing, a “cluster” is a set of loosely coupled cornputing devices that work together closely so that in many aspects they can be viewed as a single computing device. A cluster usually comprises a plurality of cluster members, or blades. A cluster member is a computing device having all the essential functional components to be considered as a computer while lacking certain features of a stand-alone device for the consideration of space, power, etc. In principle, a cluster member of a switch cluster can perform the switching function just as a conventional stand-alone switch. For example, a cluster member can handle mobile originating traffic, can receive an incoming call, can route an incoming call to the switch cluster serving the recipient subscriber of the call, and can terminate an incoming call if the recipient subscriber is served by the cluster member itself.
Applying the cluster paradigm, a switch can be configured as a switch cluster having a plurality of cluster members. Particular embodiments of the switch cluster include MSC Blade Cluster (MSC BC), MSC Server Blade Cluster (MSC SBC), etc; and accordingly, a cluster member may be an MSC blade, an MSC-S blade, etc. The cluster approach has the effect that a service area which used to be served by a stand-alone switch can now be served by a highly compact switch cluster. This provides the benefits of load balancing and high availability, to name a few. For instance, in order to keep the load for each cluster member as even as possible, a distribution mechanism distributes all subscribers served by the service area of the switch cluster over all cluster members.
Each cluster member in a switch cluster will use dedicated call-routing numbers for terminating/handing-over calls so as be able to direct the call to the correct cluster member. The particular mechanism is to assign a complete call-routing number series to a dedicated switch cluster. This has the effect that the switch cluster allocates only call-routing numbers from its own series.
The existing solution to call-routing number management suffers from various drawbacks. For example, the addition of a cluster member (e.g., for capacity increase) requires at least one additional call-routing number series. This has an impact on the configuration of the network (particularly the part outside the switch cluster) to make routing of the new call-routing number series possible in the network.
Moreover, each cluster member requires at least one call-routing number series although the capacity of the whole cluster with n cluster members may not require n call-routing number series in view of the used traffic profile. If one number series per cluster member is insufficient, at least two number series must be defined per cluster member. This at least doubles the amount of number series, although a smaller increase of the number series (e.g., 50%) may be sufficient. Other functions require a dedicated call-routing number series per entity (e.g. MSRN per Location Area). For instance, with m entities, m MSRN number series are required. In a switch cluster with n cluster members this would require n×m MSRN number series only for functional reasons, but possibly not for capacity reasons, which is clearly a waste of resources.